EP0472852B1 - Preparation of a shock resistant polyacrylic ester-polyvinylchloride graft polymer - Google Patents

Description

The invention relates to a process for the production of thermoplastic compositions consisting of vinyl chloride homopolymers or copolymers and polymers for impact modification based on polyacrylic acid esters. Compared to the prior art, an improvement in the particle size distribution, the reproducibility of the bulk density and above all the amount of wall caking was achieved during the polymerization.

The processes for producing vinyl chloride graft copolymers in suspension on rubber-elastic polymer particles produced in emulsion according to the prior art still have some disadvantages.

The production of graft polymers in which vinyl chloride is polymerized onto polyacrylic acid alkyl esters - which serve for impact modification - is known. In the patents DE-B-10 82 734, 10 90 856 and 10 90 857 processes are described in which graft polymers with about 2 to 25 percent by weight of acrylic ester rubber are obtained. In the production of such graft polymers, the reactor walls have deposits which are difficult to remove. The particle size distribution (measured with an air jet sieve) still has a fine fraction below 40 »m and a coarse fraction above 250» m. The fine fraction leads to turbidity and thus pollution of the wastewater when the suspension polymer is separated from the aqueous phase and to dust problems when handling the dry powder. The coarse fractions deteriorate the surface quality on modern high-performance processing machines.

DE-A-21 62 615 discloses the production of graft polymers of vinyl chloride onto polymers of the acrylic ester type, the end polymers containing 30 to 60 percent by weight of acrylic acid ester units. Here, the acrylic acid esters in the presence of polymerized small amounts of a polyfunctional ethylenically unsaturated monomer in emulsion. For emulsion polymerization, an emulsifier with a low HLB value (2 to 12) or a high (> 40) should be used, such as. B. the sodium salt of sulfosuccinic acid bis (tridecyl ester) (HLB = 4 to 7) or an alkyl sulfate salt with a short alkyl chain, such as sodium 2-ethylhexyl sulfate (HLB approx. 50). Vinyl chloride, a suitable suspending agent and an initiator soluble in the monomer are added to the aqueous emulsion of the rubber particles. The pH is set to 3 to 9. In order to prevent the formation of wall coverings, a highly viscous methylhydroxypropyl cellulose is preferably used. The vinyl chloride graft polymerization is carried out in suspension.

The disadvantage of this process is the use of a high molecular weight suspending agent which is difficult to handle. Furthermore, the bulk density of the graft polymers is not sufficient for the usual processing methods and in a mixture with polyvinyl chloride, the processing is carried out on, for. B. extruders get moldings with comparatively low impact strength, poor surface and low output.

EP-A-0 313 507 discloses a process in which a polymer with 70 to 40 percent by weight of polymerized units of vinyl chloride and 30 to 60 percent by weight of polymerized units of at least one acrylic acid ester and optionally further monomers copolymerizable with acrylic acid esters is obtained. In a first step, acrylic acid esters and optionally further monomers are added in aqueous emulsion with the addition of a monomer with at least two ethylenically unsaturated, non-conjugated double bonds in the presence of initiator and a water-soluble salt of a fatty acid containing 12 to 18 carbon atoms as emulsifier at an initial pH -Value from above 9 converted to a polymer with a glass transition temperature of below 0 ° C. In addition to the fatty acid salt, in the presence of at least one alkali or ammonium salt, an alkyl sulfonic acid with 8 to 20 carbon atoms and / or an alkyl acrylic sulfonic acid with 3 polymerized up to 16 carbon atoms in the alkyl radical.

In a second step, water, suspending agent, a precipitant for the emulsifiers used in the emulsion polymerization, initiator, optionally further auxiliaries and vinyl chloride are placed in the polymerization vessel and the aqueous polyacrylate dispersion is added to this.

The addition of a second emulsifier and a precipitant is disruptive in normal operations. In addition, an increased storage and filling effort is necessary.

A method has now been found which does not have the disadvantages of the methods mentioned. The end polymer is prepared in two stages, in a first stage the rubber-elastic impact modifier in an emulsion polymerization and in a second stage the monomer to be modified matrix is polymerized in the presence of the rubber-elastic particles in suspension, in the second stage that Matrix-forming monomers are introduced with the initiator, the suspension medium system and, if appropriate, additives and heated to a temperature of ≧ 30 ° C. and then the emulsion latex is fed in. For technical reasons, the emulsion latex usually has a temperature of 30 to 40 ° C.

In the first stage, at least one acrylic acid ester is polymerized in the presence of crosslinking compounds which can be copolymerized with the acrylic acid esters and have at least two non-conjugated double bonds in aqueous emulsion.

The polymerization in aqueous emulsion takes place in the presence of emulsifying salts.

Suitable acrylic acid esters are those which have a glass transition temperature in the polymer of below -20 ° C., it also being possible to use acrylic ester mixtures or else mixtures with copolymerizable monomers.

Examples of acrylic acid esters are: alkyl esters with 2 to 10 carbon atoms in the alkyl chain, such as. B. butyl acrylate, 2-ethyl-hexyl acrylate, octyl acrylate and similar acrylic acid alkyl esters, or acrylic acid alkyl aryl esters, such as. B. phenyl propyl acrylate, or acrylic acid polyether esters, such as. B. phenoxyethoxyethyl acrylate.

Examples of crosslinking substances are: (meth) acrylates of polyhydric alcohols, such as. B. ethylene glycol dimethacrylate, butylene glycol dimethacrylate, pentaerythritol tetraacrylate etc. or allyl methacrylate, or the allyl esters of polyvalent acids, such as. B. Phthalic acid diallyl ester, maleic acid diallyl ester, fumaric acid diallyl ester.

The crosslinking compounds are used in amounts of 0.1 to 5.0 parts by weight of the organic phase of the first stage, the amount being chosen so high that the gel content of the particles is 90% or more.

Suitable monomers copolymerizable with the acrylic acid esters are, for example, styrene, vinyl acetate, methacrylic acid esters with 1 to 10 carbon atoms, vinyl ether.

The emulsifying compounds which can be used are the alkali metal salts or the ammonium salt of fatty acids with 12 to 18 carbon atoms or of alkylsulfonic acids with 12 to 18 carbon atoms or of alkylarylsulfonic acids or of sulfuric acid alkyl semesters with 12 to 18 carbon atoms in the chain.

Examples include sodium laurate, sodium lauryl sulfonate, sodium dodecylbenzenesulfonaf and sodium lauryl sulfate. These are usually used in amounts of 0.3 to 2.5 percent by weight, based on the monomer of the first stage.

In initiators in the emulsion polymerization, conventional compounds such as ammonium peroxydisulfate, hydrogen peroxide, or azo compounds, such as. As azodiisobutyronitrile etc., in amounts of 0.05 to 0.5 percent by weight, based on the monomer.

If necessary, reducing compounds and metal salts which are capable of forming a redox system with the initiator can be added, such as. B. alkali sulfites, alkyl aldehyde sulfoxylates, organic acids such as ascorbic acid, and metal salts such as. B. iron sulfate and copper sulfate.

The emulsion polymerization can be carried out batchwise, continuously or semi-continuously, the method of semi-continuous polymerization being preferred.

Part of the water of the monomers, the emulsifier and the initiator (or the redox system) is initially introduced at the polymerization temperature of 40 to 90 ° C. and, after the polymerization has started, the remaining portion of the reaction mixture is added continuously or batchwise.

The polymerization is terminated at a conversion of> 99.9%. In the second stage, vinyl chloride or vinyl chloride with up to 20 percent by weight of copolymerizable monomers is polymerized onto the rubber-elastic particles produced in the first stage in aqueous suspension.

In order to obtain the advantageous properties of the end polymer, it is necessary to first prepare a suspension of VC in the aqueous phase and only then to add the emulsion latex, and it has surprisingly been found that the amount of deposits on the is only added at temperatures above 30 ° C Reactor walls is drastically lowered.

Suitable copolymerizable monomers are, for example, vinyl esters (e.g. vinyl acetate, vinyl laurate), vinyl halides (e.g. vinylidene chloride), unsaturated acids and their anhydrides (e.g. fumaric acid, maleic acid), (meth) acrylic acid and their esters (mono- and diesters) and imides of maleic acid and its N-derivatives.

The commonly used suspension medium, such as. B. hydroxyethyl cellulose, hydroxypropyl cellulose, Methyl hydroxypropyl cellulose, polyvinyl alcohols, partially saponified polyvinyl acetates, copolymers of maleic acid with alkyl vinyl ethers, polyvinyl pyrrolidone either individually or as a mixture. In addition, fatty acid esters of mono- or polyhydric alcohols, such as. B. fatty acid ethoxylates, sorbitan esters, fatty alcohol ethoxylates, are added in amounts of 0.05 to 1.0%.

The suspension polymerization is carried out in the presence of free-radical initiators which are soluble in vinyl chloride. Examples include diacyl peroxides such as dilauroyl peroxide, dibenzoyl peroxide; Dialkyl peroxides such as dicumyl peroxide; Peroxyesters such as t-butyl perpivalate, dialkyl peroxydicarbonates with isopropyl, butyl, myristyl, cyclohexyl, etc. alkyl groups; organic sulfoperic acids such as acetylcyclohexylsulfonyl peroxide; or also azo initiators, such as azobis (isobutyronitrile). The conversion of vinyl chloride should be 75 to 95%, based on the vinyl chloride used. At the desired final conversion, the remaining monomer is removed, the solid from the aqueous dispersion z. B. separated by centrifuges and the solid obtained in z. B. Dried current dryers.

When checking the wall coverings, it is noticeable that in a procedure according to the invention after the polymerization, even after several batches, only a few, easily removable caking adheres to the wall of the polymerization reactor. In a procedure not according to the invention, in which the polyacrylic ester latex was added before the vinyl chloride or after the vinyl chloride but at temperatures below 30 ° C, depending on the reactor size, caking up to several centimeters in thickness is difficult to remove and, as described, is the Significantly hinder heat dissipation during the polymerization, to be observed after only one polymerization batch.

The modified PVC powder obtained in this way is characterized by a narrow particle size distribution, high bulk density combined with favorable porosity and good entomonomerizability.

The polymers are used with polyacrylic ester proportions of up to approx. 10% with the addition of customary processing aids, pigments and optionally other additives, for example extruded, calendered, injection molded, etc., to give shaped articles.

In the case of proportions of the polyacrylic acid alkyl ester up to 40%, the mixture is usually mixed with a non-impact-modified polyvinyl chloride to a proportion of 3 to 10%, preferably 5 to 7%, and then processed as before.

The molded parts from the polymerization process according to the invention are notable for good processability, high impact strength and good surface quality.

The invention is illustrated below by Examples 1 to 3 and Comparative Examples 1 to 4.

Quellungsindex des Polyacrylatgels:

  (Gelgehalt und Quellungsindex wurden an gefriergetrocknetem Material bestimmt)
Restmonomergehalte:  Head-Space-Gaschromatographie
K-Wert des Pulvers:  DIN 53 726
Schüttgewicht:  DIN 53 468
Rieselfähigkeit:  Trichtermethode (⌀ 2 bis 16 mm)
Korngrößenverteilung:  mit Luftstrahlsieb nach DIN 53 734
Weichmacheraufnahme:  DIN 53 417
Oberfläche des Formteils:  visuelle Beurteilung
Schlagzähigkeit:  DIN 53 453, Normkleinstab gekerbtThe specified values were determined using the following methods:
Gel content of the polyacrylate: the fraction insoluble in tetrahydrofuran; Separation by centrifugation:

Swelling index of the polyacrylate gel:

(Gel content and swelling index were determined on freeze-dried material)
Residual monomer contents: head space gas chromatography
K value of the powder: DIN 53 726
Bulk weight: DIN 53 468
Free-flowing: funnel method (⌀ 2 to 16 mm)
Grain size distribution: with air jet sieve according to DIN 53 734
Plasticizer absorption: DIN 53 417
Surface of the molded part: visual assessment
Impact resistance: DIN 53 453, standard small rod notched

example 1 a) Preparation of the polyacrylic acid ester dispersion

Parts template = kg Dosage parts = kg completely desalinated water 200 = 60 100 = 30 Butyl acrylate - 99 = 29.7 Allyl methacrylate - 1 = 0.3 Ammonium persulfate 0.04 = 0.012 0.06 = 0.018 Lauric acid 0.36 = 0.108 0.54 = 0.162 Sodium hydroxide 0.083 = 0.025 0.123 = 0.037

In a 150-liter polymerization reactor equipped with a blade stirrer, the atmospheric oxygen was displaced by evacuation and gassing with nitrogen, 57 kg of fully demineralized water (DI water), 0.108 kg of lauric acid and 0.025 kg of sodium hydroxide were introduced and the mixture was heated to 80.degree.

After the solid constituents had dissolved, 12 g of ammonium persulfate dissolved in 3 kg of demineralized water were added and then 0.30 kg of the butyl acrylate / allyl methacrylate mixture. After 5 minutes, the polymerization had started, the remaining 29.7 kg of the monomer mixture and, in parallel, a solution of 0.162 kg lauric acid, 0.037 kg NaOH and 0.018 kg ammonium persulfate in 30 kg demineralized water were added within four hours. The polymerization was continued for two hours.

The following values were determined: Residual monomer content: <500 ppm (ie sales> 99.95%) Gel content of the solid: 95% Swelling index: 5 Solids content: 25.1%

b) Polymerization of vinyl chloride onto the polyacrylate

For the subsequent suspension polymerization, the following were introduced in a 235 l polymerization reactor with an impeller stirrer and a heating / cooling jacket: completely desalinated water: 112.1 parts = 89.4 kg Methyl hydroxypropyl cellulose: (viscosity 50 mPa s 2% by weight solution) 0.16 parts = 0.128 kg Sorbitan monolaurate 0.12 parts = 0.096 kg Lauroyl peroxide 0.10 parts = 0.080 kg

The atmospheric oxygen was displaced by evacuation and gassing with nitrogen. Then it was closed: Vinyl chloride: 94 parts = 75 kg
and after heating up to 32 ° C:

Polybutyl acrylate latex (19.07 kg)

Fixed share: 6 parts = 4.79 kg water content: 17.9 parts = 14.28 kg

The mixture was then heated to the polymerization temperature of 60 ° C. and polymerized at this temperature up to a vinyl chloride pressure of 3.5 bar. The mixture was then cooled, the remaining monomer was removed and the solid was separated from the aqueous phase by filtration. The filtrate was clear.

The reactor wall was free of caking.

The solid was dried in a fluid bed dryer. The following values were determined: Polyacrylate ester content: 6.7% by weight (corresponds to a vinyl chloride conversion of 89%) Sieve analysis: Proportion <63 »m: 3% Proportion> 250 »m: 2% Bulk density: 680 g / l Free flowing: 2 mm Plasticizer intake: 8 g / 100 g

Without cleaning, 20 batches were carried out in the reactor until cleaning was necessary because of caking, but the heat removal was still sufficient.

Comparative Example 1

The polyacrylic acid butyl ester latex was produced as described in Example 1. In the subsequent VC graft polymerization, in contrast to example 1, the latex was added before the vinyl chloride. The workup was also the same. The filtrate was slightly cloudy.

The reactor wall showed clear deposits. After three approaches, cleaning was necessary because the heat removal was so badly affected by the thick deposits that the internal temperature could not have been kept constant in the next batch.

The following values were determined: Polyacrylic ester content: 6.7% by weight Sieve analysis: Proportion <63 »m: 9% Proportion> 250 »m: 12% Bulk density: 640 g / l Free flowing: 2 mm Plasticizer intake: 6 g / 100 g

Comparative Example 2

The polyacrylic acid butyl ester latex was produced as described in Example 1. In the subsequent VC graft polymerization, the only difference for example 1 was that the latex was added to the batch containing vinyl chloride at 25 ° C. The reactor wall showed less caking than in Comparative Example 1, but more than in Example 1. Six polymerization batches could thus be carried out without intermediate cleaning.

The following values were determined: Polyacrylic ester content: 6.7% by weight Sieve analysis: Proportion <63 »m: 5% Proportion> 250 »m: 3% Bulk density: 680 g / l Free flowing: 2 mm Plasticizer intake: 7 g / 100 g

Example 2

The procedure was as in Example 1, but 11 parts (solid) of the polybutyl acrylate latex were added at 32 ° C. to 89 parts of vinyl chloride in deionized water suspension medium. The cellulose content was 0.20% ≙ 0.16 kg.

After drying, a powder was obtained with the following values: Polyacrylic ester content: 12.2% by weight Sieve analysis: Proportion <63 »m: 4% Proportion> 250 »m: 2% Bulk density: 650 g / l Free flowing: 2 mm Plasticizer intake: 6 g / 100 g

Without cleaning, 12 approaches were carried out until the markings became too strong.

Comparative Example 3

The procedure was as in Example 2, except that the latex was fed in at 20 ° C. Polyacrylic ester content: 12.2% by weight Sieve analysis: Proportion <63 »m: 5% Proportion> 250 »m: 4% Bulk density: 630 g / l

The pourability and plasticizer uptake were as in Example 2.

Four steps could be carried out without cleaning.

Example 3

The procedure was as in Example 1, but 35 parts (solid) of the polybutyl acrylate latex were added at 32 ° C. to 89 parts of vinyl chloride in deionized water / suspending agent. The cellulose content was 0.40%.

After drying, a powder was obtained with the following values: Polyacrylic ester content: 38% by weight Sieve analysis: Proportion <63 »m: 8% Proportion> 250 »m: 3% Bulk density: 520 g / l Free flowing: 2 mm Plasticizer intake: 35 g / 100 g

Four approaches were run without intermediate cleaning.

Comparative Example 4

The procedure was as in Example 3, except that the latex was added before the vinyl chloride.

After drying, a powder was obtained with the following values: Polyacrylic ester content: 38% by weight Sieve analysis: Proportion <63 »m: 17% Bulk density: 380 g / l Free flowing: 12 mm Plasticizer intake: 50 g / 100 g

Cleaning had to be carried out after each polymerization batch.

The powders of Examples 1 to 3 and Comparative Examples 1 to 4 were processed in an extruder with the addition of commercially available formulation components. The polyacrylic ester contents were necessarily adjusted to 6.7%, based on PVC plus polyacrylate = 100, by adding a commercially available suspension PVC (K value 68).

Profiles were produced, the surfaces of which were visually assessed and from which test specimens were made for the impact test. surface a _k kg / m² example 1 glittering 40 2nd glittering 42 3rd glossy, slightly matt 38 See Ex. 1 glittering 34 2nd glittering 38 3rd glittering 38 4th matt / streaky 15

Claims (1)

1. A process for preparing thermoplastic compositions based on vinyl chloride homopolymers or copolymers and based on polyacrylic esters which are prepared in aqueous emulsion by polymerization of acrylic esters in the presence of compounds which have a crosslinking action, are copolymerizable with the acrylic esters and have at least two non-conjugated double bonds, having a glass transition temperature below -20°C, characterized in that the vinyl chloride or vinyl chloride containing up to 20 per cent by weight of copolymerizable monomers is heated with an initiator, a suspension medium system and, if desired, additives in aqueous suspension to a temperature ≧ 30°C but below the polymerization temperature and then after addition of the polyacrylic ester latex polymerization is carried out at temperatures of from 40 to 90°C to the desired degree of conversion.